Dsandfort, first off thanks for all the inspiration. My tank models yours very closely. It if half full of RO as we speak. I used small rubber bumpers, (little stick on circles)designed for the bottom of furniture, to space my glass from the frame. This worked well giving me about 1/8 - 3/16 inch thick seal uniformly. The rubber was flexible so I didnt worry about pressure points so much. I even put 160 pounds of weights on top around the perimeter as it set. When the silicon sets, the bumbers are encased and pressure points are eliminated by the uniform seal.